Drilling tool for use in machining a conductive work piece

ABSTRACT

A drilling tool for use in machining a conductive work piece that includes a forward electrode tip including an outer radial portion and an inner radial portion. The outer radial portion includes a forward face, and the inner radial portion extends from the forward face of the outer radial portion. The drilling tool further includes a dielectric sheath that extends circumferentially about the outer radial portion, at least one side electrode coupled to the dielectric sheath, and a protective sheath that extends circumferentially about the dielectric sheath. An opening is defined in the protective sheath such that the at least one side electrode is at least partially exposed.

BACKGROUND

The present disclosure relates generally to electrochemical machining(ECM) and, more specifically, to a drilling tool for use in forming acontinuous, variable geometry bore hole within a conductive work piece.

Rotary machines, such as gas turbines, are often used to generate powerwith electric generators. Gas turbines, for example, have a gas paththat typically includes, in serial-flow relationship, an air intake, acompressor, a combustor, a turbine, and a gas outlet. Compressor andturbine sections include at least one row of circumferentially-spacedrotating buckets or blades coupled within a housing. At least some knownturbine engines are used in cogeneration facilities and power plants.Engines used in such applications may have high specific work and powerper unit mass flow requirements. Moreover, the efficiency of gasturbines is directly proportional to the temperature of exhaust gasdischarged from the combustor and channeled past the rotating buckets orblades of the turbine. As such, the extreme temperatures of the exhaustgas generally require the static and rotating turbine airfoils to bemanufactured from high temperature-resistant materials, and to includecooling features therein.

For example, turbine blades are typically cooled by channelingcompressor discharge air through a plurality of cooling channelsextending through the turbine blades. At least one known process offorming the cooling channels in the turbine blades is shaped-tubeelectrochemical machining (STEM). STEM is a non-contact electrochemicalmachining process that utilizes a conductive work piece (i.e., theturbine blades) as an anode, and an elongated drilling tube as acathode. As the conductive work piece is flooded with an electrolyticsolution, material is oxidized and removed from the conductive workpiece near the leading edge of the drilling tube. STEM is generallyeffective at forming straight cooling channels having high aspect ratioswithin a conductive work piece, such as a turbine blade. Electrochemicalmachining techniques have also been developed for forming non-linearcooling channels within turbine blades. However, contact or rubbingsometimes occurs between a drilling tool and side walls of the coolingchannels when guiding the drilling tool through the non-linear coolingchannels, thereby decreasing the service life of the drilling tool.Moreover, at least some known turbine blades are fabricated frommaterial that is not easily oxidized during an electrochemical machiningprocess such that wear of the drilling tool is further exacerbated.

BRIEF DESCRIPTION

In one aspect, a drilling tool for use in machining a conductive workpiece is provided. The tool includes a forward electrode tip includingan outer radial portion and an inner radial portion. The outer radialportion includes a forward face, and the inner radial portion extendsfrom the forward face of the outer radial portion. The drilling toolfurther includes a dielectric sheath that extends circumferentiallyabout the outer radial portion, at least one side electrode coupled tothe dielectric sheath, and a protective sheath that extendscircumferentially about the dielectric sheath. An opening is defined inthe protective sheath such that the at least one side electrode is atleast partially exposed.

In yet another aspect, a drilling tool for use in machining a conductivework piece is provided. The tool includes an electrode assemblyincluding a forward electrode tip that includes an outer radial portionand an inner radial portion. The outer radial portion includes a forwardface, and the inner radial portion extends from the forward face of theouter radial portion. The electrode assembly further includes adielectric sheath that extends circumferentially about a portion of theforward electrode tip, and at least one side electrode coupled to thedielectric sheath. A protective cap is positioned at least partiallyover the electrode assembly. The protective cap includes a first openingand a second opening defined therein such that the inner radial portionof the forward electrode tip and the at least one side electrode are atleast partially exposed.

DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings in whichlike characters represent like parts throughout the drawings, wherein:

FIG. 1 is a schematic illustration of an exemplary electrochemicalmachining system;

FIG. 2 is a cross-sectional view of an exemplary drilling tool that maybe used with the electrochemical machining system shown in FIG. 1;

FIG. 3 is a cross-sectional view of an alternative drilling tool thatmay be used with the electrochemical machining system shown in FIG. 1;and

FIG. 4 is a perspective view of an exemplary protective cap that may beused with the drilling tool shown in FIG. 3.

Unless otherwise indicated, the drawings provided herein are meant toillustrate features of embodiments of the disclosure. These features arebelieved to be applicable in a wide variety of systems comprising one ormore embodiments of the disclosure. As such, the drawings are not meantto include all conventional features known by those of ordinary skill inthe art to be required for the practice of the embodiments disclosedherein.

DETAILED DESCRIPTION

In the following specification and the claims, reference will be made toa number of terms, which shall be defined to have the followingmeanings.

The singular forms “a”, “an”, and “the” include plural references unlessthe context clearly dictates otherwise.

“Optional” or “optionally” means that the subsequently described eventor circumstance may or may not occur, and that the description includesinstances where the event occurs and instances where it does not.

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, “approximately”, and “substantially”, are notto be limited to the precise value specified. In at least someinstances, the approximating language may correspond to the precision ofan instrument for measuring the value. Here and throughout thespecification and claims, range limitations may be combined and/orinterchanged. Such ranges are identified and include all the sub-rangescontained therein unless context or language indicates otherwise.

As used herein, the terms “processor” and “computer,” and related terms,e.g., “processing device,” “computing device,” and “controller” are notlimited to just those integrated circuits referred to in the art as acomputer, but broadly refers to a microcontroller, a microcomputer, aprogrammable logic controller (PLC), and application specific integratedcircuit, and other programmable circuits, and these terms are usedinterchangeably herein. Also, in the embodiments described herein,additional input channels may be, but are not limited to, computerperipherals associated with an operator interface such as a mouse and akeyboard. Alternatively, other computer peripherals may also be usedthat may include, for example, but not be limited to, a scanner.Furthermore, in the exemplary embodiment, additional output channels mayinclude, but not be limited to, an operator interface monitor.

Further, as used herein, the terms “software” and “firmware” areinterchangeable, and include any computer program storage in memory forexecution by personal computers, workstations, clients, and servers.

As used herein, the term “non-transitory computer-readable media” isintended to be representative of any tangible computer-based deviceimplemented in any method of technology for short-term and long-termstorage of information, such as, computer-readable instructions, datastructures, program modules and sub-modules, or other data in anydevice. Therefore, the methods described herein may be encoded asexecutable instructions embodied in a tangible, non-transitory,computer-readable medium, including, without limitation, a storagedevice and/or a memory device. Such instructions, when executed by aprocessor, cause the processor to perform at least a portion of themethods described herein. Moreover, as used herein, the term“non-transitory computer-readable media” includes all tangible,computer-readable media, including, without limitation, non-transitorycomputer storage devices, including without limitation, volatile andnon-volatile media, and removable and non-removable media such asfirmware, physical and virtual storage, CD-ROMS, DVDs, and any otherdigital source such as a network or the Internet, as well as yet to bedeveloped digital means, with the sole exception being transitory,propagating signal.

Embodiments of the present disclosure relate to a drilling tool for usein forming a continuous, variable geometry bore hole within a conductivework piece. More specifically, the drilling tool includes forward “tophat” electrode tip, a dielectric sheath that extends about the forwardelectrode tip, and at least one side electrode coupled to, and embeddedwithin, the dielectric sheath. The forward electrode tip and the atleast one side electrode are oriented and have a configuration thatenables the drilling tool to form a continuous, variable-geometry borehole within the conductive work piece. As used herein,“variable-geometry” refers to dimensional changes in more than oneplane. The drilling tool further includes a protective element capableof withstanding abrasion and physical wear induced when the drillingtool is guided through and contacts side walls of the bore hole. Forexample, the protective element is embodied as either a protectivesheath or a protective cap. The protective element is designed such thatthe electrodes of the drilling tool remain exposed for electricalcommunication with the conductive work piece while also reinforcingregions of the drilling tool susceptible to abrasion and physical wear.As such, the protective element facilitates increasing the service lifeand operability of the drilling tool.

FIG. 1 is a schematic illustration of an exemplary electrochemicalmachining (ECM) system 100 for machining a conductive work piece 102. Inthe exemplary embodiment, conductive work piece 102 is coupled to amounting platform 104 positioned within an electrolyte container 106. Aswill be described in more detail below, a flow controller 108facilitates discharging a flow of electrolytic fluid 109 from withinelectrolyte container 106 towards conductive work piece 102 duringmachining operations. In the exemplary embodiment, mounting platform 104is positioned such that conductive work piece 102 is located aboveelectrolytic fluid 109. Alternatively, mounting platform 104 ispositioned such that conductive work piece 102 is at least partiallysubmerged within electrolytic fluid 109, or electrolytic fluid 109 issupplied from a source remote from conductive work piece 102.

ECM system 100 includes a power supply 110 and a drilling tool 112electrically coupled to power supply 110. More specifically, powersupply 110 is electrically coupled to conductive work piece 102, whichacts as an anode in the machining process, and to drilling tool 112,which acts as a cathode in the machining process. Material is removedfrom conductive work piece 102 when power supply 110 supplies electriccurrent to drilling tool 112 forming an applied potential acrossconductive work piece 102 and drilling tool 112. Material removed fromconductive work piece 102 by drilling tool 112 is flushed away by theflow of electrolytic fluid 109 discharged towards conductive work piece102. More specifically, flow controller 108 is coupled to a pump 114,which facilitates supplying electrolytic fluid 109 to drilling tool 112via a fluid supply line 116. As such, as will be described in moredetail below, drilling tool 112 advances within conductive work piece102 in more than one dimension along a tool path to form a bore hole 118having a variable geometry that extends through conductive work piece102 when the material is removed therefrom. More specifically, drillingtool 112 is capable of advancing within conductive work piece 102 inmore than one dimension (i.e., in a non-linear direction).

ECM system 100 also includes a robotic device 120, or any suitablearticulating member, coupled to drilling tool 112 that facilitatesadvancing drilling tool 112 along the tool path within conductive workpiece 102. In the exemplary embodiment, robotic device 120 is anysuitable computer numerically controlled device, such as a robotic endeffector, that enables drilling tool 112 to be advanced along the toolpath in a controlled and automated manner. More specifically, as will beexplained in more detail below, robotic device 120 facilitates modifyingan orientation of drilling tool 112 within bore hole 118, such that borehole 118 formed within conductive work piece 102 has a variablegeometry. Alternatively, the orientation of drilling tool 112 withinbore hole 118 is modified without the use of robotic device 120, such asmanually by an operator.

ECM system 100 may also include an inspection device 122 for performingnon-destructive inspections of conductive work piece 102. Inspectiondevice 122 is any non-destructive inspection device that enables ECMsystem 100 to function as described herein. Exemplary non-destructiveinspection devices include, but are not limited to, an ultrasonicsensing device, an X-ray testing device, and a computed tomography (CT)scanning device. Inspection device 122 operates, either continuously orat predetermined intervals, to determine at least one of the orientationof bore hole 118 formed by drilling tool 112, or a position of drillingtool 112 along the tool path. As such, a position error of drilling tool112 can be determined when the actual tool path is different from anominal tool path of drilling tool 112.

In some embodiments, ECM system 100 includes an ion sensor 124positioned proximate an outlet 126 of bore hole 118. As described above,material removed from conductive work piece 102 by drilling tool 112 isflushed away by the flow of electrolytic fluid 109 discharged towardsconductive work piece 102. Ion sensor 124 measures an ion concentrationin electrolytic fluid 109 discharged from outlet 126 of bore hole 118.In one embodiment, the ion concentration measurement is used todetermine a chemical composition of electrolytic fluid 109, whichfacilitates determining the health or operational status of drillingtool 112. Alternatively, a learning algorithm embodied within a memoryof a controller 128 is used to determine the health or operationalstatus of drilling tool 112.

In the exemplary embodiment, flow controller 108, power supply 110,robotic device 120, inspection device 122, and ion sensor 124 arecoupled in communication, by wired or wireless connectivity, withcontroller 128. Controller 128 includes a memory 130 (i.e., anon-transitory computer-readable medium) and a processor 132 coupled tomemory 130 for executing programmed instructions. Processor 132 mayinclude one or more processing units (e.g., in a multi-coreconfiguration) and/or include a cryptographic accelerator (not shown).Controller 128 is programmable to perform one or more operationsdescribed herein by programming memory 130 and/or processor 132. Forexample, processor 132 may be programmed by encoding an operation asexecutable instructions and providing the executable instructions inmemory 130.

Processor 132 may include, but is not limited to, a general purposecentral processing unit (CPU), a microcontroller, a reduced instructionset computer (RISC) processor, an open media application platform(OMAP), an application specific integrated circuit (ASIC), aprogrammable logic circuit (PLC), and/or any other circuit or processorcapable of executing the functions described herein. The methodsdescribed herein may be encoded as executable instructions embodied in acomputer-readable medium including, without limitation, a storage deviceand/or a memory device. Such instructions, when executed by processor132, cause processor 132 to perform at least a portion of the functionsdescribed herein. The above examples are exemplary only, and thus arenot intended to limit in any way the definition and/or meaning of theterm processor.

Memory 130 is one or more devices that enable information such asexecutable instructions and/or other data to be stored and retrieved.Memory 130 may include one or more computer-readable media, such as,without limitation, dynamic random access memory (DRAM), synchronousdynamic random access memory (SDRAM), static random access memory(SRAM), a solid state disk, and/or a hard disk. Memory 130 may beconfigured to store, without limitation, executable instructions,operating systems, applications, resources, installation scripts and/orany other type of data suitable for use with the methods and systemsdescribed herein.

Instructions for operating systems and applications are located in afunctional form on non-transitory memory 130 for execution by processor132 to perform one or more of the processes described herein. Theseinstructions in the different implementations may be embodied ondifferent physical or tangible computer-readable media, such as memory130 or another memory, such as a computer-readable media (not shown),which may include, without limitation, a flash drive and/or thumb drive.Further, instructions may be located in a functional form onnon-transitory computer-readable media, which may include, withoutlimitation, smart-media (SM) memory, compact flash (CF) memory, securedigital (SD) memory, memory stick (MS) memory, multimedia card (MMC)memory, embedded-multimedia card (e-MMC), and micro-drive memory. Thecomputer-readable media may be selectively insertable and/or removablefrom controller 128 to permit access and/or execution by processor 132.In an alternative implementation, the computer-readable media is notremovable.

FIG. 2 is a cross-sectional view of drilling tool 112 that may be usedwith ECM system 100 (shown in FIG. 1). In the exemplary embodiment,drilling tool 112 includes a forward electrode tip 134 that includes anouter radial portion 136 and an inner radial portion 138. Inner radialportion 138 extends from a forward face 140 of outer radial portion 136.Extending inner radial portion 138 from forward face 140 extends thefield of influence of the electric field generated by forward electrodetip 134 in a forward direction relative to drilling tool 112 whencompared to a flat electrode having a similar amount of electric currentsupplied thereto. Extending the field of influence of the electric fieldgenerated by forward electrode tip 134 facilitates increasing materialremoval from conductive work piece 102 without having to increase anamount of electric current supplied to forward electrode tip 134. Inaddition, having an outermost portion of inner radial portion 138positioned radially inward from outer radial portion 136 facilitatesreducing contact between forward electrode tip 134 and conductive workpiece 102 when bore hole 118 (shown in FIG. 1) curves within conductivework piece 102.

Drilling tool 112 also includes a dielectric sheath 142 that extendscircumferentially about outer radial portion 136, and at least one sideelectrode 144 coupled to dielectric sheath 142. At least a portion 146of dielectric sheath 142 extends beyond forward face 140 of outer radialportion 136. As such, when electric current is supplied to forwardelectrode tip 134, an electric field generated therefrom is forced totravel around portion 146 of dielectric sheath 142 prior to contactingthe side walls of bore hole 118, which facilitates balancing the removalrate of material from conductive work piece 102 positioned closest tooutermost portions of outer radial portion 136.

In an alternative embodiment, dielectric sheath 142 includes a recessedarea (not shown) sized to receive the at least one side electrode 144.The recessed area is sized such that a radially outer surface of sideelectrode 144 is substantially flush with a radially outer surface ofdielectric sheath 142. As such, side electrode 144 is embedded withindielectric sheath 142, and the likelihood of side electrode 144 fromcontacting the side walls of bore hole 118 is reduced.

Forward electrode tip 134 is oriented such that material adjacent toforward electrode tip 134 is removed from conductive work piece 102 whenelectric current is supplied to forward electrode tip 134. Removingmaterial from conductive work piece 102 adjacent to forward electrodetip 134 enables drilling tool 112 to travel in a forward direction alongthe tool path of drilling tool 112. Moreover, the at least one sideelectrode 144 is oriented such that material oriented adjacent to the atleast one side electrode 144 is removed from conductive work piece 102when electric current is supplied to the at least one side electrode144. Removing material oriented from conductive work piece 102 adjacentto the at least one side electrode 144 enables the tool path of drillingtool 112 to be directionally modified. As such, bore hole 118 (shown inFIG. 1) formed by drilling tool 112 that advances within conductive workpiece 102 has a variable geometry. Further, forward electrode tip 134and the at least one side electrode 144 may each be coupled to anindependent power supply, such that material is removed from conductivework piece 102 at different rates. In one embodiment, power supply 110has a plurality of channels that can be used to independently supply theforward electrode and at the at least one side electrode. Power supply110 is capable of supplying a steady current, or may be pulsed in anon-then-off, or high-current-then-low-current-manner.

Drilling tool 112 also includes an electrically conductive sheath 148coupled to forward electrode tip 134. Electrically conductive sheath 148extends between dielectric sheath 142 and at least a portion of forwardelectrode tip 134. More specifically, forward electrode tip 134 includesa rear portion 150 having a smaller cross-section than outer radialportion 136 of forward electrode tip 134, thereby defining acircumferential indent 152 within forward electrode tip 134. As such,electrically conductive sheath 148 extends over rear portion 150 offorward electrode tip 134, and between circumferential indent 152 anddielectric sheath 142. Moreover, electrically conductive sheath 148 hasa thickness that ensures forward electrode tip 134 is securely coupledwithin dielectric sheath 142. The thickness of electrically conductivesheath 148 is also selected to facilitate electrical bussing for forwardelectrode tip 134 with a high degree of flexibility. As such,electrically conductive sheath 148 allows sufficient electrical currentto flow therethrough that facilitates removal of material fromconductive work piece 102 while also having the flexibility to enabledrilling tool 112 to make tight radius curves when forming bore hole118.

A plurality of bussing wires (not shown) electrically couple the atleast one side electrode 144 to power supply 110. As such, forwardelectrode tip 134 and the at least one side electrode 144 areselectively, and independently, operable to form bore hole 118 having avariable geometry that extends through conductive work piece 102 whenmaterial is removed therefrom. More specifically, in one embodiment,power supply 110 supplies a first electric current to forward electrodetip 134 at a first time, and supplies a second electric current to theat least one side electrode 144 at a second time that does not overlapwith the first time. In another embodiment, power supply 110 suppliesvarying amounts of electric current to forward electrode tip 134 and theat least one side electrode 144 such that material adjacent thereto isremoved from conductive work piece 102 at different rates. Further, inan alternative embodiment, power supply 110 supplies electric current toforward electrode tip 134 and the at least one side electrode 144 suchthat vaults or turbulations (i.e., a square-shaped waveform) are formedwithin bore hole 118.

In the exemplary embodiment, drilling tool 112 also includes a flexibleguide member 154 coupled to and extending from forward electrode tip134. Flexible guide member 154 facilitates guiding drilling tool 112through bore hole 118 extending through conductive work piece 102. Asdescribed above, the forward electrode tip 134 and the at least one sideelectrode 144 are selectively operable such that bore hole 118 having avariable geometry extends through conductive work piece 102. As such,fabricating flexible guide member 154 from a flexible material enablesdrilling tool 112 to maneuver along a variable geometry tool path withinconductive work piece 102. Exemplary flexible materials include, but arenot limited to rubber, silicone, nylon, polyurethane, and latex. Aflushing channel 156 extends through flexible guide member 154 andforward electrode tip 134 and, in operation, channels a flow ofelectrolytic fluid 109 (shown in FIG. 1) therethrough. Morespecifically, flushing channel 156 is formed from a first flushingchannel 158 defined in forward electrode tip 134 and a second flushingchannel 160 defined in flexible guide member 154. As such, electrolyticfluid 109 is channeled through second flushing channel 160 and firstflushing channel 158, and discharged from a flushing aperture 162defined in inner radial portion 138 of forward electrode tip 134 toflush material removed from conductive work piece 102.

Drilling tool 112 further includes a protective sheath 164 that extendscircumferentially about dielectric sheath 142. Similar to dielectricsheath 142, protective sheath 164 also extends circumferentially aboutouter radial portion 136, and at least a portion of protective sheath164 extends beyond forward face 140 of outer radial portion 136. Assuch, protective sheath 164 is strategically positioned at a wear region166 generally defined between forward electrode tip 134 and sideelectrode 144. Moreover, dielectric sheath 142 and protective sheath 164extend such that inner radial portion 138 remains at least partiallyexposed. As such, an electric field generated by forward electrode tip134 is capable of extending from drilling tool 112 for interaction withconductive work piece 102 during operation of drilling tool 112.

Protective sheath 164 further includes an opening 168 defined thereinsuch that side electrode 144 is also at least partially exposed. Assuch, an electric field generated by side electrode 144 is likewisecapable of extending from drilling tool 112 for interaction withconductive work piece 102 during operation of drilling tool 112. In theexemplary embodiment, opening 168 is undersized relative to sideelectrode 144. Put another way, at least a portion of protective sheath164 overlaps with side electrode 144. As such, protective sheath 164facilitates retaining side electrode 144 against dielectric sheath 142.

Protective sheath 164 is fabricated from any material that enablesdrilling tool 112 to function as described herein. For example, in theexemplary embodiment, protective sheath 164 is fabricated from adielectric material such that protective sheath 164 does not interferewith operation of forward electrode tip 134 and side electrode 144.Exemplary materials that may be used to fabricate protective sheath 164include, but are not limited to, a silicone rubber material or apolyester material, such as high-density polyethylene terephthalate. Insome embodiments, the polyester material is modified to include astrengthening additive for increasing the strength of the polymer. Morespecifically, in one embodiment, the polyester material is modified byfilling interstitial spaces between monomers of the polymer chain of thepolyester with the strengthening additive. An exemplary strengtheningadditive includes, but is not limited to, titanium dioxide, acrylics,ionomers, or modified polyolefins.

FIG. 3 is a cross-sectional view of an alternative drilling tool 170that may be used with the ECM system 100 (shown in FIG. 1), and FIG. 4is a perspective view of an exemplary protective cap 172 that may beused with the drilling tool 170. In the exemplary embodiment, drillingtool 170 includes an electrode assembly 174 that includes forwardelectrode tip 134, dielectric sheath 142, and at least one sideelectrode 144. Drilling tool 170 further includes a protective cap 172positioned at least partially over electrode assembly 174. Morespecifically, protective cap 172 includes a forward wall 176 and a sidewall 178 that at least partially extend over wear region 166 generallydefined between forward electrode tip 134 and side electrode 144. Inaddition, forward wall 176 and side wall 178 are oriented relative toeach other for defining a hollow interior 180 within protective cap 172.Side wall 178 is further oriented such that protective cap 172 includesan open end 182 for providing access to hollow interior 180therethrough. As such, electrode assembly 174 is insertable through openend 182 for positioning within hollow interior 180 when assemblingdrilling tool 170.

Protective cap 172 further includes a first opening 184 and a secondopening 186 defined therein such that inner radial portion 138 offorward electrode tip 134 and side electrode 144 are at least partiallyexposed. As such, electric fields generated by forward electrode tip 134and side electrode 144 are capable of extending from drilling tool 170for interaction with conductive work piece 102 during operation ofdrilling tool 170. In the exemplary embodiment, first opening 184 isdefined in forward wall 176 and second opening 186 is defined in sidewall 178. First opening 184 is sized such that inner radial portion 138is insertable through first opening 184. In one embodiment, inner radialportion 138 extends from forward face 140 of outer radial portion 136 bya distance such that inner radial portion 138 protrudes from protectivecap 172 when inserted through first opening 184. As such, the field ofinfluence of the electric field generated by inner radial portion 138 isnot constrained by forward wall 176 of protective cap 172 duringoperation of drilling tool 170.

In addition, as described above, second opening 186 is defined withinside wall 178 for at least partially exposing side electrode 144. Secondopening 186 is undersized relative to side electrode 144 to facilitateretaining side electrode 144 against dielectric sheath 142. Moreover,electrode assembly 174 and protective cap 172 are rotationally fixedrelative to each other such that side electrode 144 remains at leastpartially exposed at second opening 186 during operation of drillingtool 170. For example, in one embodiment, electrode assembly 174 andprotective cap 172 are coupled to each other with an adhesive whenassembling drilling tool 170. In an alternative embodiment, electrodeassembly 174 and protective cap 172 are rotationally fixed relative toeach other with a mechanical interlocking feature.

Moreover, as described above, forward electrode tip 134 includes rearportion 150 having a smaller cross-section than outer radial portion 136of forward electrode tip 134, thereby defining circumferential indent152 within forward electrode tip 134. In the exemplary embodiment,circumferential indent 152 receives electrically conductive sheath 148and dielectric sheath 142. More specifically, electrically conductivesheath 148 and dielectric sheath 142 extend over rear portion 150 offorward electrode tip 134, and between circumferential indent 152 andside wall 178 of protective cap 172 to facilitate fitting electrodeassembly 174 within hollow interior 180. In an alternative embodiment,dielectric sheath 142 extends at least partially over outer radialportion 136 for further dielectrically separating forward electrode tip134 and side electrode 144.

Protective cap 172 is fabricated from any material that enables drillingtool 170 to function as described herein, such as any dielectricmaterial with suitable abrasion resistance characteristics. For example,protective cap 172 may be fabricated from a ceramic material, apolymeric material, or a composite material including a combination ofceramic material and polymeric material. In the exemplary embodiment,protective sheath 164 is fabricated from a dielectric ceramic materialsuch that protective cap 172 does not interfere with operation offorward electrode tip 134 and side electrode 144. An exemplary materialthat may be used to fabricate protective cap 172 includes, but is notlimited to, an aluminum oxide material.

In one embodiment, protective cap 172 is formed by machining a solidpiece of dielectric material into a desired shape and/or having desiredfeatures, such as hollow interior 180, first opening 184, and secondopening 186. Alternatively, protective cap 172 is formed via an additivemanufacturing technique.

An exemplary technical effect of the system and methods described hereinincludes at least one of: (a) increasing the wear resistance of an ECMdrilling tool; (b) increasing the service life of the ECM drilling tool;and (c) facilitating greater turbine efficiency through the formation ofnon-linear cooling channels in a conductive work piece, such as aturbine blade.

Exemplary embodiments of an ECM drilling tool and related components aredescribed above in detail. The system is not limited to the specificembodiments described herein, but rather, components of systems and/orsteps of the methods may be utilized independently and separately fromother components and/or steps described herein. For example, theconfiguration of components described herein may also be used incombination with other processes, and is not limited to practice withonly turbine assembles and related methods as described herein. Rather,the exemplary embodiment can be implemented and utilized in connectionwith many applications where forming non-linear holes in a conductivework piece is desired.

Although specific features of various embodiments of the presentdisclosure may be shown in some drawings and not in others, this is forconvenience only. In accordance with the principles of embodiments ofthe present disclosure, any feature of a drawing may be referencedand/or claimed in combination with any feature of any other drawing.

This written description uses examples to disclose the embodiments ofthe present disclosure, including the best mode, and also to enable anyperson skilled in the art to practice embodiments of the presentdisclosure, including making and using any devices or systems andperforming any incorporated methods. The patentable scope of theembodiments described herein is defined by the claims, and may includeother examples that occur to those skilled in the art. Such otherexamples are intended to be within the scope of the claims if they havestructural elements that do not differ from the literal language of theclaims, or if they include equivalent structural elements withinsubstantial differences from the literal languages of the claims.

What is claimed is:
 1. A drilling tool for use in machining a conductivework piece, said drilling tool comprising: a forward electrode tipcomprising an outer radial portion and an inner radial portion, saidouter radial portion comprising a forward face, and said inner radialportion extending from said forward face of said outer radial portion; adielectric sheath that extends circumferentially about said outer radialportion; at least one side electrode coupled to said dielectric sheath,the at least one side electrode configured for machining the conductivework piece, the dielectric sheath separating the forward electrode tipfrom the at least one side electrode; and a protective sheath thatextends circumferentially about said dielectric sheath, wherein anopening is defined in said protective sheath such that said at least oneside electrode is at least partially exposed through the opening formachining the conductive work piece.
 2. The drilling tool in accordancewith claim 1, wherein said protective sheath is fabricated from adielectric material.
 3. The drilling tool in accordance with claim 1,wherein said protective sheath is fabricated from one of a siliconerubber material or a polyester material.
 4. The drilling tool inaccordance with claim 3, wherein the polyester material is modified toinclude a strengthening additive.
 5. The drilling tool in accordancewith claim 1, wherein said opening is undersized relative to said atleast one side electrode.
 6. The drilling tool in accordance with claim1, wherein at least a portion of said dielectric sheath and saidprotective sheath extend beyond said forward face of said outer radialportion.
 7. The drilling tool in accordance with claim 1 furthercomprising an electrically conductive sheath coupled to said forwardelectrode tip, said electrically conductive sheath extending betweensaid dielectric sheath and at least a portion of said forward electrodetip.
 8. The drilling tool in accordance with claim 7, wherein saidforward electrode tip comprises a circumferential indent definedtherein, said circumferential indent defining said portion of saidforward electrode tip.
 9. The drilling tool in accordance with claim 7further comprising: a flexible guide member coupled to and extendingfrom said forward electrode tip; and a flushing channel extendingthrough said flexible guide member and said forward electrode tip, saidflushing channel configured to channel a flow of electrolytic fluidtherethrough.
 10. The drilling tool in accordance with claim 9, whereinsaid electrically conductive sheath extends along at least a portion ofsaid flexible guide member.